Extracting Metals with Carbon
- The Earth’s crust contains metals and metal compounds such as gold, copper, iron oxide and aluminium oxide
- Useful metals are often chemically combined with other substances forming ores
- A metal ore is a rock that contains enough of the metal to make it worthwhile extracting
- Common examples of oxide ores are iron and aluminium ores which are called haematite and bauxite respectively
- Unreactive metals do not have to be extracted chemically as they are often found as the un-combined element
- Examples include gold and platinum which can both be mined directly from the Earth’s crust
- They are known as native metals
- The position of the metal on the reactivity series determines the method of extraction
- Metals placed above carbon are extracted using electrolysis
- Lower placed metals can be extracted by heating with carbon which reduces them, two common examples being iron and carbon
The extraction method depends on the position of a metal in the reactivity series
Extraction of Copper
- Most copper ores exist as copper (II) sulfide
- The copper can be extracted in two stages
- Stage 1: The copper sulfide is heated in the air to produce the oxide
- 2CuS (s) + 3O2 (g) → 2CuO (s) + 2SO2 (g)
- Stage 2: The copper oxide is reduced by carbon
- 2CuO (s) + C (s) → 2Cu (s) + CO2 (g)
- This is an example of a redox reaction, whereby both reduction and oxidation have taken place
Extraction of Iron
- Iron is extracted in a large container called a blast furnace from its ore, haematite
- Modern blast furnaces produce approximately 10000 tonnes of iron per day
- The process is demonstrated and explained below
- The raw materials: iron ore (haematite), coke (an impure form of carbon), and limestone are added into the top of the blast furnace
- Hot air is blown in the bottom
- Zone 1:
- Coke burns i the hot air forming carbon dioxide
C (s) + O2 (g) → CO2 (g)
- Zone 2:
- At the high temperatures in the furnace, more coke reacts with carbon dioxide forming carbon monoxide
CO2 (g) + C (s) → 2CO (g)
- Zone 3:
- Carbon monoxide reduces the iron (III) oxide in the iron ore to form iron
- This will melt and collect at the bottom of the furnace, where it is tapped off:
Fe2O3 (s) + 3CO (g) → 2Fe (I) + 3CO2 (g)
- Limestone (calcium carbonate) is added to the furnace to remove impurities in the ore.
- The calcium carbonate in the limestone decomposes to form calcium oxide:
CaCO3 (s) → CaO (s) + CO2 (g)
- The calcium oxide formed reacts with the silicon dioxide, which is an impurity in the iron ore, to form calcium silicate
- This melts and collects as a molten slag floating on top of the molten Iron, which is tapped off separately:
CaO (s) + SiO2 (s) → CaSiO3 (l)